Preparation of mineral free asphaltenes

ABSTRACT

Disclosed herein is an invention directed to a method of deasphalting in which a desired amount of asphalt is removed by adjusting the solvent power of the solvent-feed system to obtain a desired cotangent theta for the system. Also disclosed is the application of the cotangent theta principle to two-stage deasphalting of Athabasca bitumen.

United States Patent Mitchell et al.

[451 Dec. 18,1973

[ PREPARATION OF MINERAL FREE 2,853,426 9/1958 Peet 208/309 AS H3,278,415 10/1966 Doberenz et al. 208/309 [75] I t D d L M h n J G S h2,871,180 1/1959 Lowman et al 208/11 nven ors: avl l c e ames peig t,

both of Edmonton, Alberta, Canada OTHER PUBLICATIONS Richard, PaperPresented at the 19th Canadian Chem- [731 Assignees. Canad a Cll-leSServlce, Ltd-; ical Engineering Conference and 3rd Symposium onlnfpeflal f 'Atlant'c Catalysts,'Oct. l9-22, 1969, Edmonton, Alberta, 17Rlchfield Canada Llmlted; Gulf 011 pages Canada Limited; part interestto each Primary Examiner-Herbert Levine 22 Filed; May 2 197 Attorney-J.Richard Geaman [21] Appl. No.: 145,662 [57] ABSTRACT Disclosed herein isan invention directed to a method [52] US. Cl 208/251, 208/1 1, 208/309of deasphalting in which a desired amount of asphalt is [51] Int. ClC10g 21/00 removed by adjusting the solvent power of the solvent- [58]Field of Search 208/1 1, 251, 309 feed system to obtain a desiredcotangent theta for the system. Also disclosed is the application of thecotan- [56] References Cited gent theta principle to two-stagedeasphalting of Atha- UNITED STATES PATENTS basca bitumen 2,188,0131/1940 Pilat et a1 208/324 7 Claims, 2 Drawing Figures c1 ,5 g 70 E B n:so 5 2 50 E -.2 -.4 -,6 -.8 I.O -l.2 -l.4 4.6 4.8 -2.0

COT 9 n/nnh u.

PATENTEUBEB 18 ms 3.779302 SHEET 10? 2 ASPHALTENES IN SYSTEMPRECIPITATED INVENTORS 9 DAVID L. MITCHELL,

ATTORNEY I BY JAMES 6. SP 16 Fig- I M PREPARATION OF MINERAL FREEASPHALTENES BACKGROUND OF THE INVENTION The present invention isdirected to a method of removing mineral contaminants from petroleumfractions. More particularly, the present invention is concerned withthe deasphalting of crude petroleum fractions and the removal of mineralcontaminants during a deasphalting operation. The invention isparticularly useful in treating bitumen recovered from bituminous sands.

Large deposits of bituminous sand are found in various localitiesthroughout the world. The term, bituminous sand, is used herein toinclude those materials commonly referred to as oil sand, tar sand andthe like. One of the most extensive deposits of bituminous sand occurs,for example, in the Athabasca District of the Province of Alberta,Canada.

Typically, the composition of these sands by weight is: from aboutpercent to about 20 percent oil; from about 1 percent to about percentwater; and from about 70 percent to about 90 inorganic solids. Thespecific gravity of the bitumen varies from about I to about 1.05 at 60F. The major portion of the inorganic solids, by weight, is a fine grainporous sand, having a particle size greater than about 45 microns andless than 2,000 microns. The remaining inorganic solid matter has aparticle size of less than 44 microns and is referred to as fines. Thefines content typically varies from about 5 percent to about 30-percentby weight of the solid inorganic content of bituminous sand. However, itis not uncommon for the composition of bituminous sand to vary from theabove-mentioned ranges. Also, in mining the bituminous sand, clay, whichis found in layers of varying thickness in such sand areas, may be mixedwith the bitumen, thus increasing the inorganic solids content,particularly the fines content of the material to be processed. Thefines portion contains minor amounts of various metals including, forinstance, titanium and zirconium. Such metals are sometimes present ineconomically recoverable concentrations. In any event, the presence ofsuch metals in recovered bitumen is frequently considered undesirable,especially in connection with upgrading of the bitumen to saleableproducts.

In refining crude petroleum, including bitumen recovered from bituminoussands, a variety of processes are available for converting the lowerboiling distillate portion of the crudes into more valuable products.Materials boiling below about 750 F. are usually recovered byatmospheric distillation and materials boiling up to 950 to l,l50 F., orhigher, by vacuum distillation. The remaining residuum generallycontains high concentrations of the high molecular weight organiccompounds with sulfur, nitrogen, oxygen, metals and other non-hydrogenspecies, as well as high molecular weight hydrocarbons, includingcondensed ring aromatics. The non-hydrocarbon compounds are oftenpoisonous to catalysts used in upgrading processes with metal compoundsor mineral contaminants being particularly deleterous to crackingcatalysts.

The residual portions of crude petroleum are sometimes described interms of relative solubility as comprising: firstly, a pentane solubleheavy oil fraction resembling distillate except for its high molecularweight and boiling point; secondly, a less soluble resin or maltenefraction; and thirdly, a pentane insoluble asphaltene fraction. The termasphaltenes" as used herein refers to material which is insoluble inpentane under temperature and pressure conditions used for theextraction. When so extracted, the asphaltenes separate as solidparticles or granules. Resins" are less clearly defined terms in the artand the term is used herein to describe that portion of the bitumenwhich adheres to the insoluble asphaltene particles, but which may besolubilized by a further extraction with pentane. The term deasphaltedheavy oil" is used herein to describe that portion of the crudepetroleum or bitumen that is solubilized by the first extraction with asolvent.

The deasphalting of petroleum crude is well known in'the art.Descriptions of deasphalting operations may be found in U. S. Pat. No.3,278,415, by Doberenz, et al; U. S. Pat. No. 2,188,013 by Pilat, et al;and U. S. Pat. No. 2,853,426, by Peet. In the above processes, the metalcontaminants are normally remove together with the resins andasphaltenes and, depending upon their origin, generally about 60 percentof the crude, by addition to the crude of an excess (from 2 to 10volumes) of a low boiling liquid hydrocarbon. Propane,

. propylene, normal or isobutanes, butylenes, normal or isopentanes,hexanes, or their mixture, light straight run naphthas, or other lightaromatic free fractions of mineral oil have been claimed to besatisfactory solvents.

However, the above art teaches that the crude or asphaltic materialsyield low recoveries of deasphalted heavy oil, generally below 40percent of the residuum, and it has been stated that if high ratios ofsolvent to crude are utilized, to obtain oil yields above about 60percent, excessive amounts of metal compounds and some asphaltenesappear in the extract phase.

It is an object of the present invention to provide a process for theremoval of metal contaminants from an Athabasca bitumen using normallyliquid or liquefied hydrocarbon solvents.

It is a further object of the present invention to provide a processwhereby hydrocarbon solvents, for example the isomeric and paraffinichydrocarbons having from three to eight carbon atoms, saturatedsubstituted or unsubstituted cycloparaffins having five or more carbonatoms are utilized to deasphalt petroleum crude.

It is still a further object of the present invention to provide aprocess for deasphalting the Athabasca bitumen whereby the deasphaltingmedium is adjusted by the addition thereto of any of the aforementionedsolvents employed either individually or as blends of two or moreindividual solvents.

It is still a further object of the present invention to provide aprocess whereby a low mineral content asphaltene fraction is producedwhich may be employed in the manufacture of high grade metallurgicalcoke, electrocarbon, or other processes wherein a low mineral content isa necessary prerequisite.

With these and other objects in mind, the present invention may be morefully understood by specific referral to the following discussion anddrawings.

SUMMARY OF THE INVENTION The objects of the present invention areaccomplished by a process for treating an asphaltene containingpetroleum crude which may be contaminated by both metals and water. Thepetroleum crude may con tain a considerable water concentration, beingrepresented by a froth. The process comprises the introduction,singularly or in multiple steps, of a normally liquid or liquefiedhydrocarbon solvent into the asphaltene containing petroleum crude so asto adjust the total asphaltene solvent power of the system. Byasphaltenes is meant those hydrocarbons which are pentane insolubles. Bysolvent power of the system is meant the ability of the totalhydrocarbon system, including solvent, to dissolve and contain theasphaltenes present.

In general, the process uses hydrocarbon solvents which may be selectedfrom the group consisting of one or more paraffinic or isomerichydrocarbons having from three to eight carbon atoms and saturatedsubstituted cycloparaffins and saturated unsubstituted cycloparaffinshaving five or more carbon atoms. The solvent power of the systemincluding solvent and feed is adjusted by latering the proportions ofthe solvent or the solvent type according to the required cotangent 6,

as described hereafter, so as to yield a desired solvent power for thetotal system of solvent and petroleum crude. In general, in treatingpetroleum crude, for example an Athabasca bitumen, it is preferred thatfrom about 5.0 to about 40.0 barrels of solvent are introduced in eachstep of the process per barrel of liquid to be treated.

In a two-step process, a solvent having a high solvent power isintroduced to form two fractions. The first fraction preferably containsabout 10.0 to about 25 weight percent of the asphaltenes and resinscontained within the petroleum crude, at least 85.0 weight percent ofthe water and at least 98.0 weight percent of the mineral contaminants.A liquid fraction or heavy oil is formed which contains the remainingmineral contaminants and asphaltenes originally present in the petroleumcrude. Subsequently, the two fractions are separated and a secondnormally liquid or liquefied hydrocarbon solvent forming a low solventpower system is introduced into the liquid fraction, thereby forming twoadditional liquid fractions. A first additional liquid fraction isformed containing the remainder of the water, mineral contaminants andasphaltene content of the heavy oil and a second additional liquidfraction is formed consisting essentially of a mineral, water andasphaltene free heavy oil. These two additional liquid fractions arethen separated to form the desired products of the present invention,that is, a heavy oil significantly free of water or mineral contaminantsin a solvent phase and an asphaltene fraction of the bitumensubstantially free of mineral and water contaminants.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention may be morefully understood by referral to the following drawings in which:

FIG. 1 represents the relationship between as phaltene percent recoveryand the Cot of the total system for determining solvent type andquantity of solvent introduced for use in the process of the presentinvention; and

FIG. 2 represents one embodiment ofa two-step process utilizing thesolvent power relationship of the present invention for treating apetroleum crude to remove the asphaltenes therefrom and concentrate andremove the metal contaminants and water.

DETAILED DESCRIPTION OF THEINVENTION Solvent power is generally measuredas the solubility of an oil in a particular solvent system. As theasphaltenes are the least soluble components of the oil, it is necessaryto define solvent power as the measurement of the critical solubility ofthe asphaltenes in given oil systems containing solvents so thatdeasphalting and deimineralizing of asphaltene containing oils may beregulated. Conventional deasphalting processes for the deasphalting ofheavy oils by pentane or other paraffinic solvents generally utilize thesolvents singularly, wherein the asphalts are all concentrated in onedeasphalting tower, but in most instances the asphaltenes recoveredhaving a high mineral content.

It has been found that particularly useful solvent combinations may beformed by the mixing of one or more high power solvents with heavy oilsin definite relationships, so that exact precipitation of asphaltenes indeasphalting tower occurs. Specifically, the yield of asphalteneprecipitate obtained from the heavy oil is related to solubility of thenormally precipitating asphaltenes in the solvent system. The majorinfluence on precipitation is governed by the solvent power of thesingle solvent or solvent blend, in conjunction with the heavy oilsystem, with the contribution of the solvent powers of the soluble oilsand resins in the heavy oil being considered. Additional informationconcerning solubility characteristics may be found in Regular Solutionby Hildebrand and Scott, published by Prentice Hall in 1963 (Library ofCongress Catalogue No. 62-1 1984).

The relationship of asphaltene solvent power of the heavy oil-solventprecipitating medium may be expressed by the solubility parameterContangent 0 (Cot 0). Cot 0 is derived from experimental data in whichthe percent asphaltenes precipitated from a system for each solvent orsolvent blend mixture with the heavy oil is plotted against theindividual solvent concentrations or blend concentrations in the system,thereby deriving a definite linear relationship. Cot 6 being thecontangent of the angle 0 formed between the X-axis or the axiscontaining the solvent concentration and the linear line formed by theexperimental data. The Cot 0 relationship and means for determining 0for deasphalting system is fully presented by J. A. Bichard, OilSolubility, 19th Canadian Chemical Engineering Conference and 3rdSymposium on Catalysis, Oct. l9-22, I969, Edmonton, Alberta. Asoriginally conceived, the Cot 0 relationship was intended to provide ameans for insuring that undesirable precipitation would not occur. Usingthis concept, it was found that precipitation would be precluded bymaintaining the Cot 0 of the system at a positive value. It has now beenfound that by use of the Cot 0 relationship, solvent power relationshipsmay be placed on a single functional graph as illustrated by FIG. 1. Onemay choose the desired percent of asphaltenes to be precipitated fromFIG. 1 and thereby determine what Cot 6 relationship is required for thesystem, thus adjusting the solvent content of the system to the exactspecifications required to obtain the necessary Cot 0 relationship inthe system and thereby control the degree of precipitation ofasphaltenes.

The significance of selecting Cot 0 for deasphalting becomes apparentwhen one realizes that a solvent system exhibiting a negative valueyields an excellent asphaltene precipitation. If the solvent systemexhibits a very low solvent power, its respective Cot 0 is liable to lieclose to the X-axis and exhibit a value of minus infinity. If the systemexhibits a good solvent power, it

will lie closer to the Y-axis. A good solvent has a positive value bydefinition, the cotangent 6 having a value greater than zero. Therefore,a solvent having a cotangent 0 less than zero will be a relatively poorsolvent. It is preferred that the cotangent 0 of the solvent and oilsystem utilized in the deasphalting of heavy oil be less than aboutminus 0.3 if a significant degree of asphaltene precipitation isdesired.

To fully understand the meaning of solvent power for the Athabasca oilsystems, it is necessary first to consider the components, compositionand structure of the oil. The existence of saturates, aromatics, resinsand asphaltenes in the oil has been measured showing the oil to be amixture of isogels or heterogels, a structure composed of an orderedstate consisting of asphaltenes surrounded by still higher molecularweight aromatic type hydrocarbons with layers of resin molecules aboutthem. These molecules form micelles in an oil saturated environment.Weak inner molecular attraction and repulsion forces between thenonpolar hydrocarbons are essentially responsible for the structure. Theprocess of solution proceeds by the addition of solvent toward thenucleus. These components held by the weakest association forcesdissolve first. The energy supplied to overcome the association forcesof the micelles is supplied by the solution energy of the solventsystem. The solution energy is different for different solvent systemsand is a function of chemical structure. Paraffin containing solventsystems have the least amount of solution energy, with solution energydecreasing with increasing molecular size, this is due apparently toparallel selfassociation.

Polarizability of aromatics, such as benzene, result in greaterdispersion forces and hence, high solution energy. This is even moreprevalent with condensed aromatics with side chain substitution. Partialmoments through substitution are responsible for the good solvent powersof chlorinated solvents. When the solution energy of thesolvent-molecules is insufficient to overcome the strong cohesive forcesacting on the nucleus of the micelle, floculation or precipitation ofthese nuclei occur. The experimental end point of asphaltene solubilityis a measure of-the critical cohesive energy of the system at which thesolvation of the nuclei can no longer be maintained and precipitation ofthe asphaltene occurs. Therefore, in deasphalting it is desirable toobtain the effective rate of floculation required such that the exactCot 0 or solvent blend in the oil system may be chosen whereby anexacting percent asphaltene will be precipitated in the deasphaltingtower. In multiple stage deasphalting for the treatment of materialssuch as metal contaminated Athabasca bitumens, it is preferred that thefirst deasphalting tower exhibit a rel atively low asphalteneprecipitation with a high precipitation of the minerals containedtherein. Between about -0.3 and O.6 Cot 0 would be preferred in thefirst deasphalting tower, while the second-and subsequent deasphaltingtowers would utilize a lower Cot 0 such as between about 0.3 and 2.0,preferably between about -l .4 and 2.0 so that a significantprecipitation of asphaltenes, comparatively mineral-free, will beobtained with a low asphaltene content in the oilsolvent mixtureeffluent produced from the top of the deasphalting tower. 4

Through use of FIG. 1, in which is illustrated the relationship ofasphaltene yield and solvent power of the precipitating medium asexpressed as a solubility parameter Cot 0, it has been shown that themore concentrated the solution of the bitumen in the solvent, the morelimited the solvent power of the system becomes so that the solventcannot retain as large a quantity of the asphaltenes. As bitumen oftencontains considerable'aromatic constituents, which act in a similarmanner as the added solvents, these properties must also be consideredin obtaining the Cot 0 of the solvent system shown in FIG. 1. The Cot 6of the system is a function of the type and amount of solvent utilized,as well as the type and amount of oil being treated.

In the processing of Athabasca tar sands for the formation of usefulrefinery products, one finds aresidual product of asphaltenes and ashcontent being made up of mineral contaminants in a water froth mixture.This mixture is extremely difficult to decompose into the desirableproduct of a heavy oil for coking or catalytic cracking and asphaltenesfree from minerals. The minerals are recovered for their economic valueand the asphaltenes separated as a suitable source for asphalt andderivative materials for use in commercial processes. Required is asolvent dilution technique whereby the heavy oils and asphaltenes may beseparated and the asphaltenes then separated from the minerals containedtherein for the reduction of the bitumen froth to commercially desirableproducts.

In accordance with a preferred embodiment of the invention, a heavycrude oil such as Athabasca bitumen which is contaminated by substantialamounts frequently exceeding 3 weight percent of mineral contaminants istreated in a two-stage process to produce substantially deasphaltedheavy oil and an asphaltene product sufficiently free of minerals to beuseful in the manufacture of metallurgical grade coke. In the firststage, the feedstock is contacted with hydrocarbon solvent of a type andquantity chosen to adjust the Cot 0 of the system to between about O.3and about O.6. This results in two first stage product fractions, one ofwhich is an asphaltene fraction comprising between about 10 and about 25weight percent of the asphaltenes present in the feedstock (in the caseof Athabasca bitumen frequently between about 0.5 and about 10 wt.percent of the total bitumen) and which contains more than about wt.percent, preferably more than about 98 wt. percent, of the totalminerals content of the feedstock. The second first-stage productfraction is a heavy oil fraction which contains the remainder of theasphaltenes and solvent. Where the feedstock is Athabasca bitumen, thisfraction usually contains between about 90 and about 98 wt. percent ofthe total bitumen feedstock and less than 0.1 percent of the mineralsoriginally present in the bitumen. This heavy oil fraction is thensubjected to a second-stage deasphalting treatment with hydrocarbonsolvent in which the solvent power of the system is adjusted to a Cot 0less than about 0.3 and preferably less than about 0.8 to produce asecond-stage asphaltene precipitate containing less than about 0.5 wt.percent minerals and which is therefore of sufficiently low mineralcontent for use in the manufacture of metallurgical coke. In order toobtain maximum yields of such substantially mineral-free asphaltenes, itis preferred that the Cot 6 of the secondstage deasphalting unit bemaintained less than about l.4, preferably between about l.4 and 2.0 toinsure precipitation of at least 90 and preferably 98-100 percent of theasphaltenes present in the second-stage feed. Maintaining the Cot 0 ofthe system less than about 1 .6, may result in precipitation of somematerials such as resins which are soluble in pentane in addition toprecipitation of pentane-insoluble asphaltenes. Where Athabasca bitumenis the original feed, the second-stage asphaltene product frequentlywill be equivalent to between about 5 and about wt. percent of theoriginal bitumen. The other second stage product is, of course, adeasphalted heavy oil fraction which is substantially free of mineralsand preferably also substantially free of asphaltenes and therefore doesnot present problems during further refining operations.

In another preferred embodiment of the invention, material such asAthabasca bitumen having a high water content, as well as a high mineralcontent, is treated by a two-stage process similar to that describedabove. For instance, in typical processes for recovery of bitumen fromAthabasca tar sands, the bitumen is recovered in the form of a frothcontaining between about 5 and about wt. percent by water. In treatingsuch a froth by the two-stage process described immediately above, themajority and usually between 85 and 100 percent of the water presentwill be found in the first-stage asphaltene product. It can thus be seenthat the treatment of such bituminous froth as described above has theadded advantage of removing water, as well as minerals, from the usefulproducts, i.e., the second stage deasphalted heavy oil product andsecondstage asphaltene product, thus eliminating the need for separateprocessing steps for removal of water.

In practicing the invention, from about 0.5 to about 40 barrels perbarrel of oil treated of either isomeric paraffin hydrocarbons havingfive or more carbon atoms or saturated or unsaturated substitutedcycloparaffm hydrocarbons are frequently used to adjust the solventpower of the deasphalting system. The invention relates to the use ofany one or more of the aforementioned hydrocarbon types to adjust thesystems solvent power in the enhancement of the deasphalting process.The deasphalting process is preferably conducted at from about 50 F. toabout 140 F. and at atmospheric pressure.

To more fully understand the process of the present invention, FIG. 2 ispresented in which a two-step deasphalting and demineralizing processfor treating bitumen recovered from tar sands is depicted. In theprocess, bitumen 101 is introduced simultaneously with a hydrocarbonsolvent 102 into a deasphalting tower 103. The solvent power of thissystem is preferably adjusted to a Cot 0 of between about O.3 and about0.6. A solvent-heavy oil mixture 105, containing the majority of theasphaltenes, is produced from the top of the deasphalting tower 103 andan asphaltic residue 104, preferably containing greater than 90 percentof the minerals, is produced from the lower portion of the deasphaltingtower 103. The solvent-heavy oil stream 105 is then introduced into asecond deasphalting tower 107 simultaneously with additional hydrocarbonsolvent 106. For maximum recovery of mineral-free asphalt, the solventpower of the second-stage deasphalting system is preferably adjusted toa Cot 0 between about 1 .4 and 2.0. A solvent-oil mixture 109 isproduced from the top of deasphalting tower 107 and asphalt 108, beingsubstantially mineral-free, is produced from the lower portion thereof.The solvent-oil mixture 109 is then fed to a fractionating tower l 10from which a mineral free-cracking stock oil 111 is produced from thelower portion thereof and solvent vapor 112 is produced from the upperportion thereof. The solvent vapor is then introduced into a condensor113 from which a liquid solvent stream 114 is produced. The liquidsolvent stream may be used for solvent 102 and solvent 106 makeup in thefirst and second deasphalting towers 103 and 107, respectively.

To exhibit the use of solvent power adjustment of the system to controlthe yield of precipitated asphaltenes, the following Examples arepresented:

EXAMPLE I The solvent powers in terms of Cot 0 of various systems ofsolvents and oils were detennined by mixing one-to-one volumes ofnormally liquid or liquefied solvents with an Athabasca bitumencontaining 17 wt. percent asphaltenes. A measured amount of 100 grams ofeach solvent was poured into 130 grams of a waterbitumen froth,equivalent to 100 grams of dry bitumen. The mixture was shakenvigorously for 5-l 0 minutes at 0.5 hr. intervals and allowed to settle;this procedure was conducted for approximately 8 hours. At the end ofthe 8 hour period the fractions were easily separated by decantationfollowed by filtration, with light suction of the solvent/heavy oilsolution.

After removal of any residual solvent by blowing, the water content ofthe asphaltene fraction was determined by the standard ASTM D-9558method for the determination of water in petroleum products. For theheavy oil fraction formed, the solvent was removed by blowing followedby evaporation and the water separated mechanically.

Results of this analytical procedure are set forth in Table l asfollows:

TABLE I Results of Deasphalting Bitumen Solvent Power Weight Percent ofSystem Asphaltencs Solvent (Cot 0) Precipitated Propane (2.5 to 100 3.5)est Butane 2 I00 N-Pentane l.5 I00 Hexane isomers l .2 Hcptane Isomersl.l 67 Pcntanc/Hexane l.3 83 Pentane/Heptane l .2 75Pentane/Cyclopentane ([11) 0.7 35 Pcntane/Cyclohexane (1:1) O.7 35Cyclopentane 0. I l Cyclohcxane 0 O Hcptanc/Cyclopentane (lzl) O.5 22Hcptene/Cyclohcxane (lzl) O.5 23

EXAMPLE 2 A solution of bi-constituent solvent consisting of liquidpropane and varsol was utilized in a sample of Athabasca tar bitumen inorder to determine the percent asphaltenes precipitated. As liquidpropane itself precipitates asphaltenes plus resins and possibly otherfraction of bitumen, initial concentrations with percent propane solventwere determined. Yields of precipitated materials ranged from between 40to 48 percent with liquid propane used in large excess. The solution ofthe propane with varsol produced a solvent blend of increased solventpower. Consequently, the yield of precipitated material decreased. Forexample, a solvent bitumen weight ratio of 3.5 to l and a propane-varsolconcentration of 2.5 to 1 resulted in a 30.7 percent yield ofprecipitate at a Cot 0 of 2.6. In a similar manner, when bitumen waspresent in a higher concentration, the contribution of the solublearomatic portion was added to the solvent power, the precipitating mediain the yield of precipitating material decreased as the Cot value of thesystem increased. In the second case, an approximate propane-varsolweight ratio of between 1.5 and 3.5 to i was blended as a solvent. Thebitumen ratio was between l.() and 1.6 to l as compared to four to onein the first instance andthe Cot 0 was -2.5. The yield of precipitatingmaterial was 18.4 percent in this case, showing considerable decrease inprecipitate as compared to the 30.7 percent as illustrated in the firstcase.

Therefore, it can be seen through this experimentation and FIG. 1 thatthe amount of asphaltene precipitate can be varied over a wide range,from say, approximately 0.5 percent to 100 percent of the totalasphaltene content of the system, dependent upon the adjusted solventpower of the precipitating medium or solvent system. The inherentadvantage of this control is that subsequent crops of asphaltenes can beprecipitated as essentially mineral-free material in a seconddeasphalting tower with the majority of the minerals precipitated with afirst crop of material in a first deasphalting tower.

The process of the present invention discloses a technique wherebysuitable solvents such as paraffinic and isomeric hydrocarbons havingfrom three to eight carbon atoms and saturated substituted orunsubstituted cycloparaffins having five or more carbon atoms may beblended in exacting compositions of solvents for the use in thedeasphalting of bitumen or petroleum crudes containing mineral and watercontaminants and high asphaltene concentrations.

The present invention has been described herein with respect toparticular embodiments and aspects thereof and it will be appreciated bythose skilled in the art that various changes and modifications can bemade, however, without departing from the scope of the presentinvention.

Therefore, we claim:

1. A process for deasphalting a petroleum crude oil feedstock containingasphaltenes and mineral contaminants which comprises:

a. contacting said petroleum crude with hydrocarbon solvent in a firstdeasphalting zone maintained at a cot 0 solubility parameter betweenabout 0.3 and about -0.6, whereby between about and about 25 wt. percentof the asphaltenes are precipitated together with about 90 to 100 wt.percent of the mineral contaminants; and

b. recovering said precipitate from said first deasphalting zone;

0. recovering from said first deasphalting zone a heavy oil fractioncontaining between about 75 and about 90 wt. percent of the asphaltenesoriginally present in the feedstock and less than 10 wt. percent of themineral contaminants present in such 'feedstock;

d. contacting said heavy oil fraction from the first deasphalting zonewith hydrocarbon solvent in a sec- 0nd deasphalting zone wherein the cot0 solubility parameter is maintained less than about O.8;

e. recovering from said second deasphalting zone an asphaltene fractioncontaining between about and about 90 wt. percent of the asphaltenesoriginally contained in the feedstock together and less than about 0.5wt. percent of the mineral contaminants present in such feedstock; and

f. recovering a deasphalted heavy oil fraction from the seconddeasphalting zone.

2. The process of claim 1 in which the hydrocarbon solvents areformulated as a single solvent or solvent blend selected from the groupconsisting of paraffinic or isomeric hydrocarbons having from three toeight carbon atoms, saturated substituted cycloparaffins having five ormore carbon atoms and saturated unsubstituted cycloparaffins having fiveor more carbon atoms with the concentration of the solvent or solventblend introduced to form the system adjusted by altering the proportionsof the solvent used according to the requisite Cot 0 so as to yield thedesired Cot 6 for the system.

3. The process of claim 1 in which the feedstock is bitumen recoveredfrom bituminous sand, which bitumen contains between about 0.5 and about10 wt. percent asphaltenes and at least about 3 wt. percent minerals.

4. The process of claim 3 in which the feedstock also contains betweenabout 5 and about 30 wt. percent water and in which at least aboutpercent of such water is recovered in the first asphaltene fraction.

5. A process for deasphalting a petroleum crude oil feedstock containingasphaltenes and mineral contaminants which comprises:

a. contacting said petroleum crude with hydrocarbon solvent in adeasphalting zone maintained at a cot 0 solubility parameter betweenabout 0.3 and about 0.6, whereby between about 10 and about 25 wt.percent of the asphaltenes are precipitated together with about to wt.percent of the mineral contaminants; and

b. recovering said precipitate from said deasphalting zone.

6. The process of claim 5 in which the hydrocarbon solvents areformulated as a single solvent or solvent blend selected from the groupconsisting of paraffinic or isomeric hydrocarbons having from three toeight carbon atoms, saturated substituted cycloparaffins having five ofmore carbon atoms and saturated unsubstituted cycloparaffins having fiveor more carbon atoms with the concentration of the solvent or solventblend introduced to form the system adjusted by altering the proportionsof the solvent used according to the requi site cot 0 so as to yield thedesired cot 0 for the system.

7. The process of claim 5 in which the feedstock is bitumen recoveredfrom bituminous sand, which bitumen contains between about 0.5 and about10 wt. percent asphaltenes and at least about 3 wt. percent minerals.

2. The process of claim 1 in which the hydrocarbon solvents are formulated as a single solvent or solvent blend selected from the group consisting of paraffinic or isomeric hydrocarbons having from three to eight carbon atoms, saturated substituted cycloparaffins having five or more carbon atoms and saturated unsubstituted cycloparaffins having five or more carbon atoms with the concentration of the solvent or solvent blend introduced to form the system adjusted by altering the proportions of the solvent used according to the requisite Cot theta so as to yield the desired Cot theta for the system.
 3. The process of claim 1 in which the feedstock is bitumen recovered from bituminous sand, which bitumen contains between about 0.5 and about 10 wt. percent asphaltenes and at least about 3 wt. percent minerals.
 4. The process of claim 3 in which the feedstock also contains between about 5 and about 30 wt. percent water and in which at least about 85 percent of such water is recovered in the first asphaltene fraction.
 5. A process for deasphalting a petroleum crude oil feedstock containing asphaltenes and mineral contaminants which comprises: a. contacting said petroleum crude with hydrocarbon solvent in a deasphalting zone maintained at a cot theta solubility parameter between about -0.3 and about -0.6, whereby between about 10 and about 25 wt. percent of the asphaltenes are precipitated together with about 90 to 100 wt. percent of the mineral contaminants; and b. recovering said precipitate from said deasphalting zone.
 6. The process of claim 5 in which the hydrocarbon solvents are formulated as a single solvent or solvent blend selected from the group consisting of paraffinic or isomeric hydrocarbons having from three to eight carbon atoms, saturated substituted cycloparaffins having five of more carbon atoms and saturated unsubstituted cycloparaffins having five or more carbon atoms with the concentration of the solvent or solvent blend introduced to form the system adjusted by altering the proportions of the solvent used according to the requisite cot theta so as to yield the desired cot theta for the system.
 7. The process of claim 5 in which the feedstock is bitumen recovered from bituminous sand, which bitumen contains between about 0.5 and about 10 wt. percent aSphaltenes and at least about 3 wt. percent minerals. 